1. Field of the Invention
The present invention relates to force sensors. The force sensors of the invention are also capable of monitoring force generated by pressure. The force sensors can also be used as pressure sensors.
2. Description of the Related Art
FIG. 20 shows a cross-section of a conventional pressure sensor 1. FIG. 21 shows a cross-section along the line XXI—XXI of FIG. 20. FIG. 22 shows an electric circuit realized by using the pressure sensor 1. As shown in FIG. 20, the pressure sensor 1 has a structural body 21. The structural body 21 has a force transfer block 40 and a sensor block 30. As shown in FIG. 21, a surface of the sensor block 30 has four resistive elements 32a-32d. Adjoining resistive elements are mutually connected. For example, ends of the resistive elements 32a and 32b mutually connect. Four electrodes 34a-34d are formed on the surface of the sensor block 30. Each electrode 34a-34d connects with a connecting member of each adjoining resistive element. For example, the electrode 34b is connected with the connecting members of the resistive elements 32a and 32b. The four electrodes 34a-34d are connected with terminals 12a-12d respectively via wires 16a-16d. As shown in FIG. 20, the four terminals 12a-12d lead to the exterior of the pressure sensor 1. The force transfer block 40 covers the four resistive elements 32a-32d. As shown in FIG. 22, the four resistive elements 32a-32d form a full-bridge electric circuit.
The greater the force operated upon the pair of resistive elements 32b and 32d, the greater the change in the resistance values thereof. By contrast, the resistance values of the pair of resistive elements 32a and 32c hardly change when greater force is operated thereon. In this specification, the resistive elements 32b and 32d, wherein resistance values change in accordance with a greater force being operated thereon, are called piezoresistive elements. Of the four resistive elements comprising the full-bridge electric circuit, the pair of resistive elements 32b and 32d are piezoresistive elements. Consequently, when a force pushing the force transfer block 40 against the surface of the sensor block 30 changes, the balance of the full-bridge electric circuit changes. As shown in FIG. 22, in a state whereby a constant current flows between the electrodes 34d and 34b, the magnitude of the force operated upon the force transfer block 40 can be measured by measuring an electric potential V1 of the electrode 34c or an electric potential V2 of the electrode 34a. 